Home » Public Forums » GMCnet » Alternator follies (I think it's a bad alternator, but...)
| Alternator follies [message #212208] |
Tue, 25 June 2013 14:58  |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Senior Member |
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I just picked up my GMC from storage, getting it ready for a trip with the grandkids to a lake near Williams, AZ (read "30 degrees cooler than Mesa, AZ). The engine battery was stone cold dead when I got there, but it fired off the charge that was left on the house batteries with the boost switch on.
The alternator light glowed dull red all the way home, so to be safe I ran the generator. Got it washed, inspected (necessary to renew the plates) and home without incident.
Here's what I'm seeing with the engine running, and dash A/C on max, after some time charging the engine (chassis) battery with the PD converter.
Engine battery: drops to around 12 volts (keeps dropping if I don't plug the charger in)
Engine battery sense lead at alternator: 12 volts (mimics the battery voltage)
Brown (resistor) sense wire at alternator: 10.4 volts
Output (big red wire) at alternator: 10.4 volts.
Thing is, with little or no load, the alternator will put out 14 volts, give or take. And I noticed that when I cycle the A/C off, the alternator output jumps up over 15 volts for a split second. Also, turning on just the headlights will drop the alternator output by a volt or so.
I'm thinking it's about 98% likely that the alternator (rebuilt Delco 80A unit installed in 2009 by the PO) is cooked, but I'm very willing to hear dissenting opinions at this point (while I let the engine compartment cool down so I can even get to the alternator without spontaneously combusting). Thanks, all!
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: Alternator follies [message #212209 is a reply to message #212208] |
Tue, 25 June 2013 15:05  |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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| habbyguy wrote on Tue, 25 June 2013 12:58 |
I just picked up my GMC from storage, getting it ready for a trip with the grandkids to a lake near Williams, AZ (read "30 degrees cooler than Mesa, AZ). The engine battery was stone cold dead when I got there, but it fired off the charge that was left on the house batteries with the boost switch on.
The alternator light glowed dull red all the way home, so to be safe I ran the generator. Got it washed, inspected (necessary to renew the plates) and home without incident.
Here's what I'm seeing with the engine running, and dash A/C on max, after some time charging the engine (chassis) battery with the PD converter.
Engine battery: drops to around 12 volts (keeps dropping if I don't plug the charger in)
Engine battery sense lead at alternator: 12 volts (mimics the battery voltage)
Brown (resistor) sense wire at alternator: 10.4 volts
Output (big red wire) at alternator: 10.4 volts.
Thing is, with little or no load, the alternator will put out 14 volts, give or take. And I noticed that when I cycle the A/C off, the alternator output jumps up over 15 volts for a split second. Also, turning on just the headlights will drop the alternator output by a volt or so.
I'm thinking it's about 98% likely that the alternator (rebuilt Delco 80A unit installed in 2009 by the PO) is cooked, but I'm very willing to hear dissenting opinions at this point (while I let the engine compartment cool down so I can even get to the alternator without spontaneously combusting). Thanks, all!
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Mark,
Given the fact that your battery was stone dead when you first picked up the coach, I would be looking at the battery as the culprit here. I'm guessing it has a dead short and one of the cells is completely dead, not allowing it to take a charge. I would start there as it doesn't make sense that the alternator would just die while in storage.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Alternator follies [message #212210 is a reply to message #212209] |
Tue, 25 June 2013 15:10 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Senior Member |
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Carl, I guess that's certainly a possibility. My concern was that the battery (after charging) was able to produce at least 12 volts at the same time the alternator output dropped to only 10.4 volts. I'd think 12 volts at the battery sense line would be enough to get the alternator putting out "real voltage", wouldn't it?
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: Alternator follies [message #212214 is a reply to message #212210] |
Tue, 25 June 2013 15:28 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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I guess so, Mark. But a dead battery will do some strange things. I'm no expert on electrical systems and have only a rudimentary understanding of how the alternator, sense wire, etc work, but if I were you, I would be getting the chassis battery checked first, and if it's bad, replacing it before I bought a new alternator. JWIWD
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Alternator follies [message #212223 is a reply to message #212208] |
Tue, 25 June 2013 16:11 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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It sounds like a slipping alternator belt or a bad battery. It also could be a couple of blown diodes in the alternator.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Alternator follies [message #212228 is a reply to message #212208] |
Tue, 25 June 2013 17:20 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Senior Member |
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Thanks for the input and the advice, guys... I just went out and double-checked the voltage, and didn't have the boost switch on (so the chassis/engine battery wasn't charging). I'll give it some more charge time to see if it behaves any different (and like a good battery), then move on to troubleshooting the alternator, depending on what I find.
I believe I will be replacing that alternator though, since I am pretty certain that even with only 12.0 battery volts, the alternator should put out a lot more than 10.5 volts under load.
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: Alternator follies [message #212235 is a reply to message #212208] |
Tue, 25 June 2013 17:51 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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The alt should be putting out 14.2. I'll bet that battery is done as you can't run them dead, leave them that way with a parasitic load for months so it's dead dead and then hope to charge it back to health. Plus your heat factor leads to a short life. If that battery has the wrong impedance( low or high) it won't act to stabilize the system and may have taken out the alt and or isolator which you need to test. Metering a 12v battery at 12v means it is Basically dead. Should be about 12.6v which is a huge difference.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Alternator follies [message #212239 is a reply to message #212208] |
Tue, 25 June 2013 19:38 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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You can see if the internal regulator in the alternator is defective by using a small screwdriver to ground a metal tab in the rear of the alternator while the engine is running. Look in your shop manual under alternator check out and it will show you the location of the tab and how to test it. If the voltage increases during this test with a load on the battery you will need a new regulator if the voltage stays low the alternator has other problems. Also the dio trio is a common part to go bad in the alternator these parts come in an alternator repair kit at Napa and others I haven't bought a kit in a long time so I don't know if they stock them.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Alternator follies [message #212245 is a reply to message #212208] |
Tue, 25 June 2013 20:02 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Senior Member |
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All great input and advice.
I'm not the most patient guy in the world, and decided to pull the alternator and see what I could see.
The short answer - it wasn't an alternator any more - it was a paperweight. The bearings were shot (though not horribly, wobbly bad... just noisy). And it was electrically shot as well. I went to Autozone (since I needed one today) and got a rebuilt 100 amp unit ($102 out the door). Now with the A/C on I'm getting over 13 volts at idle, and almost 14 volts with some rpm, so I think it's safe to say that I should be good to go.
And yes, I do get a little belt squeal when I have everything turned on AND blip the throttle (and it's still bringing the chassis battery up to speed). But I can live with that for now, and will consider that double pulley sometime in the future. I think I might just spray on some belt dressing in the mean time to keep the slippage to a minimum.
I'm hoping my chassis battery will live through the abuse - it is only about a year old, so if it does die, I should be well inside the warranty period.
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: Alternator follies [message #212260 is a reply to message #212245] |
Tue, 25 June 2013 21:43 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Senior Member |
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| habbyguy wrote on Tue, 25 June 2013 18:02 |
All great input and advice.
I'm not the most patient guy in the world, and decided to pull the alternator and see what I could see.
The short answer - it wasn't an alternator any more - it was a paperweight. The bearings were shot (though not horribly, wobbly bad... just noisy). And it was electrically shot as well. I went to Autozone (since I needed one today) and got a rebuilt 100 amp unit ($102 out the door). Now with the A/C on I'm getting over 13 volts at idle, and almost 14 volts with some rpm, so I think it's safe to say that I should be good to go.
And yes, I do get a little belt squeal when I have everything turned on AND blip the throttle (and it's still bringing the chassis battery up to speed). But I can live with that for now, and will consider that double pulley sometime in the future. I think I might just spray on some belt dressing in the mean time to keep the slippage to a minimum.
I'm hoping my chassis battery will live through the abuse - it is only about a year old, so if it does die, I should be well inside the warranty period.
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Congrats on getting it all figured out. Keep an eye on that battery. They can't take too many deep discharges like that. If you notice it getting weak, replace it.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: [GMCnet] Alternator follies [message #212262 is a reply to message #212250] |
Tue, 25 June 2013 22:03 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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My local Autozone has those pulleys under the counter. When I asked for one on my new (rebuilt) AZ alternator, he removed the one I had and replaced it with a double one for no charge. They had a whole selection of pulleys under the counter. If for some reason you want to keep the original, those pulleys are only $6.00 or $8.00 at the auto parts store.
You could have put on the double pulley when you got the alternator and only used one groove for now. Then later you can install the second belt.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: Alternator follies [message #212272 is a reply to message #212208] |
Wed, 26 June 2013 00:21 |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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Senior Member |
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I believe that the belts the PO installed are all somewhat undersize. None of them seem to ride high in the pulleys, so I think my best option going forward would be to get a set of new belts and swap 'em all out. This is one of those things that I'll probably put off 'til fall though - it's really no fun crawling around the engine compartment when it's WAY over 100 degrees in the coach.
The toughest part of the process was getting any real tension on the alternator belt - there's really no obvious way to torque it (I ended up using a pry bar in the rear slot, pushing against the bottom of the mounting bracket slot and the bottom of the alternator). Not pretty, but adequate I guess.
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: [GMCnet] Alternator follies [message #212275 is a reply to message #212272] |
Wed, 26 June 2013 05:08 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
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Senior Member |
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This is one of those things that I'll probably put off 'til fall though
this is one of those things to do when you find it, and when you come home.
not good to fix before you are about to leave
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> The toughest part of the process was getting any real tension on the
> alternator belt -
this is the easy way
http://www.bdub.net/bovee/BoveeProducts.pdf
remember, it is the mounting bolts that hold the belts tight, the
tensioners only help set the tension during the tensioning process.
while you are there, get the sounders also, for turn signals, and leaving
lights on..
gene
> there's really no obvious way to torque it (I ended up using a pry bar in
> the rear slot, pushing against the bottom of the mounting bracket slot and
> the bottom of the alternator). Not pretty, but adequate I guess.
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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| Re: [GMCnet] Alternator follies [message #212287 is a reply to message #212208] |
Wed, 26 June 2013 07:20 |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Expired alternator is my bet, specifically an open diode or two. Specifics really don't matter, take the alternator to AutoZone and have them test it. >if< it's in warranty, ask the PO where he bought it (If it's AutoZone or Advance, alls you need is P.O.'s name and phone number and they'll have it in their system), and get a replacement. Out of warranty or no info, iof it tests bad, get another. There's no magic in it beyond having the proper pully on it. (The magic of ther system is in the sense line, and the isolator)
--johnny
'76 23' transmode norris
'76 palm beach
________________________________
From: Mark <mark@habcycles.com>
To: gmclist@temp.gmcnet.org
Sent: Tuesday, June 25, 2013 3:58 PM
Subject: [GMCnet] Alternator follies
I just picked up my GMC from storage, getting it ready for a trip with the grandkids to a lake near Williams, AZ (read "30 degrees cooler than Mesa, AZ). The engine battery was stone cold dead when I got there, but it fired off the charge that was left on the house batteries with the boost switch on.
The alternator light glowed dull red all the way home, so to be safe I ran the generator. Got it washed, inspected (necessary to renew the plates) and home without incident.
Here's what I'm seeing with the engine running, and dash A/C on max, after some time charging the engine (chassis) battery with the PD converter.
Engine battery: drops to around 12 volts (keeps dropping if I don't plug the charger in)
Engine battery sense lead at alternator: 12 volts (mimics the battery voltage)
Brown (resistor) sense wire at alternator: 10.4 volts
Output (big red wire) at alternator: 10.4 volts.
Thing is, with little or no load, the alternator will put out 14 volts, give or take. And I noticed that when I cycle the A/C off, the alternator output jumps up over 15 volts for a split second. Also, turning on just the headlights will drop the alternator output by a volt or so.
I'm thinking it's about 98% likely that the alternator (rebuilt Delco 80A unit installed in 2009 by the PO) is cooked, but I'm very willing to hear dissenting opinions at this point (while I let the engine compartment cool down so I can even get to the alternator without spontaneously combusting). Thanks, all!
--
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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